1. Field of the Invention
The present invention relates to riser management systems. More particularly, the present invention relates to a system, program product, and related methods for controlling a well during an emergency.
2. Description of Related Art
A problem presented by offshore hydrocarbon drilling and producing operations conducted from a floating platform or vessel is the need to establish a sealed fluid pathway between each borehole or well at the ocean floor and the work deck of the vessel at the ocean surface. This sealed fluid pathway is typically provided by a drilling riser system. Drilling risers, which are utilized for offshore drilling, extend from the drilling rig to a blowout preventer (BOP) which is directly or indirectly connected to an upper portion of a subsea wellhead. A typical marine drilling riser permits passage of drill pipe which is used for pumping lubricating mud down the well during drilling operations, return of drilling mud that has been pumped through the drill pipe into the main tube of the riser, and any associated drill cuttings, and provides a connection of the drilling vessel to the well above the subsea BOP stack. Similarly, production risers extend from and provide communication between the subsea wellhead system and the floating vessel.
The BOP, often referred to as a BOP stack, is a specialized valve or set of valves used to control and monitor the subsea well. The BOP stack generally includes two categories of blowout preventers: ram and annular. The ram-type BOP typically uses a pair of opposing steel rams which can extend radially to either block or open a fluid passageway extending through the BOP stack. The ram BOP includes pipe rams, blind rams, shear rams, and blind sheer rams. Pipe rams close, around the pipe to restrict flow in the annulus between the outside of the drill pipe and inner bore of the BOP stack when a drilling pipe is extending, through the bore of the BOP stack. Blind rams, which have no openings for tubing, close off the bore completely when no drilling pipes extend through the BOP stack by pressing against each other to form a seal. Shear rams and blind shear rams cut through the drilling pipe with hardened steel shears. The annular BOP functions similar to a sphincter,
The different preventers can have different closure diameters to accommodate for either the existence of drilling pipe or different diameters of drilling pipe. The BOP stack also includes a number of choke and kill lines that extend alongside the riser and enter the interior of BOP at different points between BOP elements which can be used to shut down the subsea well.
The drilling riser can be disconnected from the well above the 130P stack, allowing the drilling vessel to retrieve the riser and temporary move from the drill site should the need arise (i.e., during a hurricane event, or a malfunction). Having remained atop the wellhead, when functioning properly the BOP stack provides for containment of a live well while the vessel is not on location. Upon return, the vessel can deploy the riser, reconnect to the BOP stack, and reestablish hydrocarbon communication with the well,
The marine drilling riser also permits control of the well during an emergency through use of the BOP stack, Emergencies requiring activation of components of the BOP stack are typically associated with drilling through a zone with geological fluid pressure that is substantially higher than that which the drilling mud can contain. During such events, one or more of the different types of preventer of the BOP stack is hydraulically functioned to close off or restrict the flow of well fluid flowing through the BOP stack. Well control is then re-established by pumping an appropriate density mud through the kill line and eventually circulating it back to the surface via the choke line.
Recent newsworthy events, however, have highlighted that BOPs can have reliability issues. In a recent event, failure of the BOP to activate resulted in destruction of the drilling, rig and substantial environmental damage due to the failure of the BOP stack to stop well fluid flow into the surrounding ocean. Accordingly, recognized by the inventors is that there needs to be a two fault system in place and a wellhead based emergency control apparatus can advantageously provide the necessary fault protection by providing an independent, safe guard system. Also recognized by the inventors is that currently existing well control systems do not provide for a. wellhead based method for shutting, off a well. Recognized by the inventors, therefore, is the need for a wellhead-based systems, apparatus, and methods of controlling the flow of well fluid in an emergency that is independent of the BOP. Specifically, recognized by the inventors is the need for systems, apparatus, and methods which can include an emergency well fluid shutoff assembly positioned separately from the BOP stack which can radially compress casing strings and/or drilling pipe extending through the subsea wellhead without shearing in order to obtain a substantial reduction in the flow of well fluid through the subsea wellhead. Also recognized by the inventors is the need for systems, apparatus, and methods which include an emergency well fluid diversion assembly to divert well fluid from within the wellhead housing to an external conduit to thereby release fluid pressure of well fluid flowing within the wellhead housing in a. controlled manner.